The 'Part of Me' singer - who allegedly fell out with her best friend last October because of the 'Stay' singer's reconciliation with Chris Brown, who is still on probation for beating her in 2009 - reached out to Rihanna on her 25th birthday on Wednesday (20.02.13) and admitted she was sorry she wasn't with her to celebrate.
In a message on her Twitter profile, the 28-year-old popstar wrote: ''HAPPIEST 25TH BIRTHDAY to my baby girl @Rihanna! I wish I could b there drinking Mai-Tais & telling haters to eat a d**k w/u (sic).''
Rihanna retweeted the message with her fans, hinting she and Katy have mended their relationship after they recently avoided each other at the Grammy Awards.
Katy reportedly made a special request to be seated no where near Chris and Rihanna at the bash in Los Angeles earlier this month.
A source said: ''They aren't tight anymore because Katy doesn't approve of Rihanna dating Chris Brown.''
The last time Katy and Rihanna were spotted hanging out together was at the MTV Video Music Awards in September during which Rihanna shared a public peck on the lips with Chris for the first time since their 2009 break-up.
Meanwhile, Rihanna also shared an old black and white picture of her and Chris taken at her 20th birthday.
She captioned the picture: ''#throwbackRiRi my surprise 20th birthday party!! Im an old bitch now! Thank God for His gift and His endless mercies #25 #MilestoneLife (sic)''